FIG. 1 is a perspective cross-section view schematically showing an example of an image sensor.
The image sensor comprises a semiconductor layer 1 having a first surface F1, called front surface, supported by a stack of insulating layers 4 having an interconnection structure 5 arranged therein, and having a second surface F2, called rear (or back) surface, intended to receive an illumination and coated with an insulating layer 7. Insulating layer 7, semiconductor layer 1, and the stack of insulating layers 4 rest on a support 9, the stack of insulating layers 4 extending between semiconductor layer 1 and support 9. Interconnection structure 5, only a portion thereof being shown, is formed of portions of conductive layers 11 and of vias 13, some of which interconnect portions of conductive layers 11.
In a central portion of the sensor, the semiconductor layer comprises an array of pixels 15. Each pixel 15 comprises various electronic components (not shown), particularly a photosensitive component such as a photodiode, and one or a plurality of transistors formed on the side of front surface F1 of the semiconductor layer. At the level of front surface F1, the electronic components of the pixels are in contact with vias 13 of interconnection structure 5. On the side of rear surface F2 of the semiconductor layer, each pixel 15 is topped with a color filter 17 resting on upper surface F2′ of insulating layer 7, or rear surface of the sensor.
The sensor comprises insulated connections 19 formed at the periphery of pixel array 15. Each insulated connection 19 is formed from an opening 21 extending from rear surface F2′ of the sensor all the way to front surface F1 of semiconductor layer 1. A metal layer 23 coats the bottom and the lateral walls of opening 21 and partly extends over rear surface F2′ of the sensor to form a pad 24 therein. All across the thickness of the semiconductor layer, metal layer 23 is separated from the semiconductor layer by an insulating cladding 25. At the bottom of the opening, metal layer 23 is in contact with a portion of conductive layer 11 via one or a plurality of vias 13 of interconnection structure 5. Thus, pad 24 is electrically coupled with one or a plurality of electronic components formed in semiconductor layer 1.
FIG. 1 is not drawn to scale and, in practice, in top view, openings 21 have lateral dimensions, currently a side length or diameter from 20 to 100 μm, much larger than the lateral dimensions of pixels 15, which generally having a side length from 1 to 5 μm.
To manufacture the sensor of FIG. 1, the various electronic components of the sensor are formed from front surface F1 of semiconductor layer 1, after which interconnection structure 5 and the stack of insulating layer 4 are formed on surface F1. The assembly of semiconductor layer 1 and of the stack of insulating layers 4 is then mounted on support, or handle, 9 as shown in FIG. 1. Then only, openings 21 are formed by reactive ion etching from rear surface F2′ of the sensor all the way to front surface F1 and a metal layer 23 is deposited and etched to form insulated connections 19 and pads 24. Finally, color filters 17 are formed on rear surface F2′ of the sensor by successive steps of deposition and etching of one or a plurality of layers.
A sensor of the type in FIG. 1 and its manufacturing method have various disadvantages, at least some of which are desired to be overcome.